(1) Field of the Invention
The present invention relates to microcapsules filled with a solution containing cycloheximide (hereinafter referred to simply as CHI) and preparations thereof, and more specifically it relates to microcapsules filled with CHI and their preparations in which drawbacks of a conventional CHI crystal practically employed as rodent repellents and antimicrobials for plants are overcome.
(2) Description of the Prior Art
As conventional products to which the technique of microcapsules is applied, there are many examples such as pressure-sensitive copying papers, heat-sensitive recording papers, medicines, animal medicines, argicultural chemicals, preventive medicines against epidemics, fertilizers, cosmetics and adhesives
Further, examples in which the microcapsule technique is applied to insecticides are also present in various forms, and for example, the following preparations are known:
(a) a warfarin raticide (trade name Raze) PA1 (b) an ant repellent (trade name Merexbait) PA1 (c) cockroach insecticide (trade name Diazinon MC; suspension) and PA1 (d) a white ant repellent.
Of these preparations, the raticide in the preceding paragraph (a) is encapsulated for the purpose of causing rats to easily eat the warfarin raticide, and the ant repellent in the preceding paragraph (b) is also encapsulated for the improvement in a residual effect of the toxic food agent for ants.
In addition thereto, there is also known the encapsulation of microbiological agricultural chemicals and virus agricultural chemicals which have the residual effect and which can adjust the release of a component, but the technique of encapsulating CHI has been found nowhere.
The mechanism of the rodent-repellent effect of CHI can be presumed as follows: Rats dislike the taste of CHI and are extremely repelled by it. Once the rats have experienced this taste, they will have, in memory, a peculiar odor of CHI which human beings do not feel, and will afterward keep away from CHI by the odor alone.
Next, reference will be made to use examples of a conventional CHI crystal in which the above-mentioned rodent-repellent effect of CHI is utilized.
One example in which the CHI crystal is used is a rodent-repellent cable cover. Such cable covers can be made by kneading the CHI crystal into polyvinyl chloride (PVC) in order to give a rodent-repllent treatment to PVC, and by molding and processing it. A temperature and a time necessary for the molding is 150.degree. to 200.degree. C. and 10 to 30 minutes, respectively, and it has been confirmed that a repellent effect, i.e., an activity (hereinafter referred to as potency) of CHI is deteriorated owing to the heat treatment and/or is lost because of a presence of hydrogen chloride generated in the PVC manufacturing process and a remaining free hydrochloric acid. For this reason, if the rodent-repellent cables having the sufficient potency are contemplated, the CHI crystal must be used in a previously increased amount However, this strategy is not economical from the fact that the CHI crystal is a very expensive reagent. That is the reason why providing CHI with heat resistance and chemical resistance is required The same may be said of rodent-repellent coating compositions which are materials for the rodent-repellent cable covers.
Additionally, even after the manufacture of the rodent-repellent cables, there are problems such as a transfer (bleeding phenomenon) of the CHI crystal present in the PVC toward the surfaces of the cable covers along with the lapse of time, a deterioration in the rodent-repellent effect due to the outflow of the dissolved CHI crystal from the cable covers, and inconveniences from the viewpoints of safety and sanitation for men who handle the cables In consequence, the CHI preparations in which no bleeding phenomenon occurs in PVC are now desired.
Another example in which the CHI crystal is employed is a CHI coating composition. In general, such CHI coating compositions are directly applied on objects for which the rodent-repellent treatment is necessary. In this case, the CHI potency would decline owing to chemical properties of the objects to be applied thereon, and if the objects are articles which are used outdoors, the CHI crystal will be dissolved out with rainwater because of being water-soluble, with the result that the rodent-repellent effect will be lost. That is the reason why supplying CHI with water resistance is required.
It has also been confirmed that CHI will lose its potency in an aqueous solution with time (in the case of the aqueous CHI solution having a pH of 7, 100% of the potency was lost at 37.degree. C. in 3.5 months). Accordingly, CHI must be provided with water resistance and alkali resistance, when desired. Furthermore, since CHI is decomposed with soil-borne bacteria, the property of being resistant to the soil bacteria is also to be given thereto, if utilized as agricultural chemicals.
As be definite from the foregoing, when used in the form of crystal, CHI is very unstable and will lose the potency by its properties themselves, depending upon its usage. The employment of a large amount of CHI which is expensive is not economical, and thus it is fair to say that CHI is very inconvenient to deal with.